Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $50.47   4.132%   $52.5554   $52.56   $52.55   $52.60  
  Purchase #2 $183.44   5.721%   $193.9346   $193.93   $193.95   $193.90  
  Purchase #3 $225.82   5.527%   $238.3011   $238.30   $238.30   $238.30  
  Purchase #4 $28.37   12.617%   $31.9494   $31.95   $31.95   $31.90  
  Purchase #5 $99.30   9.266%   $108.5011   $108.50   $108.50   $108.50  
  Purchase #6 $179.84   9.391%   $196.7288   $196.73   $196.75   $196.70  
  Purchase #7 $249.97   6.415%   $266.0056   $266.01   $266.00   $266.00  
  7 purchase totals = $1,017.21       $1,087.9760   $1,087.98   $1,088.00   $1,087.90